Flexible printed wiring boards are widely used to incorporate circuits into complicated mechanisms of electronic devices, such as mobile phones, video cameras, and notebook computers, which are rapidly becoming smaller with higher functionality. Owing to their excellent flexibility, flexible printed wiring boards are also used to connect a movable part such as a printer head to a control unit. These electronic devices require electromagnetic wave shielding, and flexible printed wiring boards for use in these devices are now increasingly provided with electromagnetic wave shielding (hereinafter such flexible printed wiring boards also referred to as “shielded printed wiring boards”).
A common shielded printed wiring board usually includes a substrate film sequentially including a base film, a printed circuit, and an insulating film; and a shielding film including a conductive layer, a shielding layer laminated on the conductive layer, and an insulating layer laminated on the conductive layer, wherein the shielding film covers the substrate film such that the conductive layer is in contact with the substrate film.
The printed circuit includes a ground circuit, and the ground circuit is electrically connected to a chassis of an electronic device for grounding.
As described above, the substrate film of the shielded printed wiring board includes the insulating film on the printed circuit including the ground circuit. In addition, the substrate film is covered by the shielding film including the insulating layer.
Thus, it is required to form a hole in advance in a portion of the insulating film and a portion of the shielding film in order to electrically connect the ground circuit to the chassis of the electronic device.
This has been a factor that hinders printed circuit design flexibility.
Patent Literature 1 discloses a shielding film including a cover film formed by coating on one side of a separate film; a shielding layer including a metal thin layer and an adhesive layer provided on a surface of the cover film; and a ground member, wherein the ground member includes, on its one end, a projection connected to the shielding layer through the cover film by being pressed onto the cover film, and the other end of the ground member is exposed and formed connectable to its nearby ground portion.
In the production of the shielding film disclosed in Patent Literature 1, the ground member is pressured against the cover film such that the projection of the ground member penetrates through the cover film. Thus, the ground member can be mounted on any position of the shielding film.
Use of such a shielding film to produce a shielded printed wiring board makes it possible to electrically connect the ground circuit to the chassis of the electronic device at any position.